Nadia has taken 6 quizzes and her average score so far is 85. If she gets 100, a perfect score, on the remaining 3 quizzes, what will her new average be?
If she gets 100 on the remaining quizzes, the sum of her scores will be $6 \cdot 85 + 3 \cdot 100 = 810$ Her overall average will then be $810 \div 9 = 90$.